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MathGroup Archive 2001

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Interactive simplifying

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31913] Interactive simplifying
  • From: "Steve Gray" <stevebg at adelphia.net>
  • Date: Tue, 11 Dec 2001 01:33:52 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

    I am trying to do something like this:
Solve[Sqrt[a*z+b] + Sqrt[c*z+d] + Sqrt[e*z+f] == g, z] ,
which on first try gives an answer with about 10,000 terms. In addition, the
output is all messed up. Totally useless.
    Thinking to help it along, I used the common trick of putting one of the
Sqrt's on the right side, squaring the whole thing, collecting the Sqrt's on
one side, squaring, and doing it again until no sqrts are left. This gives a
complicated but not impossible 4th degree polynomial in z (with about 400
terms of a,...,g to various low powers), which with good substitutions of
new simplifying parameters is manageable.
    I did this with Mathematica's help but in a very awkward way: I got a
partial answer, saw what the best next step would be, cut and pasted part of
the expression onto a new line, added parentheses and squarings here and
there, manually transposed with proper sign changes, etc. This worked and
was not too painful but is very prone to error.
    I thought that M. would have Transpose and other operators to help, or
even select-and-drag with automatic sign change and other "corrections."
    There oughta be a better way. Anyone? Thanks in advance for any help.



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